The present invention relates to a method for decomposing a halogenated organic compound, and more particularly, to a method for decomposing a halogenated organic compound contained in soil such as polychlorodibenzo-p-dioxins (PCDD), polychlorodibenzofurans (PCDF), and coplanar polychlorobiphenyl (PCB) (These materials are hereinafter generally referred to as "dioxins".) with good operation property and high efficiency.
In incineration plants such as those for municipal waste, dioxins precursors (precursors for the dioxins) including organic compounds such as phenols, benzene and acetylene, chlorinated aromatic compounds such as chlorophenols and chlorobenzenes, and chlorinated alkyl compounds are formed during incineration. When flyash coexists with the dioxins precursors, the precursors change to the dioxins under the catalytic action of the flyash, and the generated dioxins exist in incineration ash. Also, the generated dioxins sometimes contaminate the incineration plant and ambient soil therearound.
Conventional technologies for decomposing dioxins in soil include a method using supercritical state water, a method using ozone or ultraviolet rays, a method by heating, a method utilizing special fungi such as "Maitake" or "Enokidake" or wood-rotting bacteria, and a method using a catalyst.
Conventional methods for decomposing dioxins contained in flyash are as follows;
(1) To keep dioxins-containing flyash for 1-2 hours at a temperature between 320 and 400.degree. C. under a reductive atmosphere such as nitrogen (for instance, 2 hours at 320.degree. C. or 1-1.5 hours at 340.degree. C.) (Hagenmaier process, "ORGANOHALOGEN COMPOUNDS Vol. 27 (1996)" p.147-152); PA1 (2) Heating dioxins-containing flyash at 300-500 .degree. C. under the existence of a dioxins formation inhibitor (JPA 4-241880).
However, all of the above-mentioned methods for decomposing dioxins contained in soil have problems in decomposition efficiency or treating operation. Especially, the method using ultraviolet rays offers a low decomposition efficiency as the rays are effective only at the irradiated surface. Also, the method using catalysts has difficulties in treating operation. The method by heating has problems of recombination and evaporation of dioxins, and the method using bacteria has low decomposition efficiency.
The methods described in the above items (1) and (2) for decomposing dioxins contained in flyash have a drawback that their high treatment temperature and long treatment time require much energy and high cost. Especially, in the above mentioned method (1), it is required to carry out the treatment under a reductive atmosphere such as nitrogen gas, bringing about complexity and a high cost.